This application relates to commonly-owned, PCT Patent Application No. PCT/US99/18610 filed Aug. 16, 1999.
The invention relates generally to systems for measuring air pressure in pneumatic tires of vehicles and, more particularly, to systems including a sensor and a transponder associated with each of the vehicle tires.
Safe, efficient and economical operation of a motor vehicle depends, to a significant degree, on maintaining the correct air pressure in the tires of the motor vehicle. Failure to correct promptly for faulty/abnormal (typically low) air.pressure may result in excessive tire wear, blow-outs, poor gasoline mileage and steering difficulties.
The need to monitor tire pressure is highlighted in the context of xe2x80x9crun-flatxe2x80x9d (driven deflated) tires, tires which are capable of being used in a completely deflated condition. Such run-flat tires, as disclosed for example in commonly-owned U.S. Pat. No. 5,368,082, incorporated in its entirety by reference herein, may incorporate reinforced sidewalls and mechanisms for securing the tire bead to the rim to enable a driver to maintain control over the vehicle after a catastrophic pressure loss, and are evolving to the point where it is becoming less and less noticeable to the driver that the tire has become deflated. The broad purpose behind using run-flat tires is to enable a driver of a vehicle to continue driving on a deflated pneumatic tire for a limited distance (e.g., 50 miles, or 80 kilometers) prior to getting the tire repaired, rather than stopping on the side of the road to repair the deflated tire. Hence, it is generally desirable to provide a low pressure warning system (LPWS) within the vehicle to alert (e.g., via a light on the dashboard, or a buzzer) the driver to the loss of air in a pneumatic tire.
FIG. 1 illustrates a typical low pressure warning system (LPWS) 100 of the prior art installed on a motor vehicle 102 (shown in dashed lines) having four pneumatic tires 104a . . . 104d installed on four respective wheels (not shown). A transponder (xe2x80x9cTAGxe2x80x9d) 106a . . . 106d is associated with each of the tires 104a . . . 104d, respectively.
As used herein, a xe2x80x9ctransponderxe2x80x9d is an electronic apparatus (device) capable of both receiving and transmitting radio frequency signals, and impressing variable information (data) in a suitable format upon the transmitted signal indicative of a measured condition (e.g., tire pressure) or conditions (e.g., tire pressure, temperature, revolutions), as well as optionally impressing fixed information (e.g., tire ID) on the transmitted signal, as well as optionally responding to information which may be present on a signal which is received by the transponder.
xe2x80x9cPassivexe2x80x9d transponders are transponders powered by the energy of a signal received from an external xe2x80x9cinterrogatorxe2x80x9d apparatus. xe2x80x9cActivexe2x80x9d transponders are transponders having their own power supply (e.g., a battery), and include active transponders which remain in a xe2x80x9csleepxe2x80x9d mode, using minimal power, until xe2x80x9cwoken upxe2x80x9d by a signal from an interrogator.
The transponders 106a . . . 106d are suitably passive transponders which obtain their operating power from an RF signal which is provided by an on-board interrogator 108 which is mounted within the vehicle.
The interrogator 108 comprises an RF transmitter 112 (e.g., for powering passive transponders), an RF receiver 114, control logic 116 which may include a microprocessor (xcexcP), and a display device 118 such a visual display and optionally including an audible alarm. Antennas (xe2x80x9cANTxe2x80x9d) 110a . . . 110d are disposed on the vehicle 102, preferably adjacent the tires 104a . . . 104d, respectively, such as in the wheel wells of the vehicle. The antennas 110a . . . 110d are suitably ferrite loopstick antennas.
The use of multiple vehicle antennas 110a . . . 110d, each at a fixed position on the vehicle adjacent a respective tire 104a . . . 104d, such as in the wheel well, is well known, and is disclosed in U.S. Pat. Nos. 3,553,060; 3,810,090; 4,220,907; 4,319,220; and 5,774,047, all of which are incorporated in their entirety by reference herein. In this manner, close coupling can be effected between the tire transponders and the vehicle antennas, thereby facilitating identifying which of the several wheels on a vehicle has a sensed low pressure condition.
In use, the interrogator 108 powers the transponders 106a . . . 106d which, in turn, transmit data indicative of a measured condition (e.g., tire air pressure) back to the interrogator 108. In any such system, it is desirable to have efficient and effective coupling of signals between the fixed antennas 110a . . . 110d (alternatively, one centrally-located fixed antenna) and the moving (i.e., when the vehicle is in motion) transponders (each of which has its own antenna, not shown).
Low pressure warning systems for tires are generally well known, and representative examples may be found in the following U.S. Patents, all of which are incorporated in their entirety by reference herein: U.S. Pat. No. 3,694,803 (Strenglein; 1972); U.S. Pat. No. 4,067,235 (Markland, et al.; 1978); U.S. Pat. No. 4,334,215 (Frazier, et al.; 1982); and U.S. Pat. No. 5,335,540 (Bowler, et al.; 1994).
An important feature of a viable low pressure warning system employing transponders and an interrogator is providing effective coupling of radio frequency (RF) signals between the transponders which may be located inside of the pneumatic tires, and the interrogator which may be located at some central location in the vehicle. An additional important feature of a viable low pressure warning system is providing an indication to the operator of the vehicle of the condition being monitored, for example, low tire pressure, correct tire pressure, etc.
For example, a straightforward approach is to have an RF transmitter and pressure sensor within each tire (e.g., affixed to the valve stem thereof). In order to save power, the transmitter may only transmit when pressure drops below a threshold value. A single, centrally-located receiver in the vehicle cab can detect the transmission, and cause an audible signal to be sounded to alert the driver to the sensed low pressure condition. In such a system, the RF transmissions from the transmitters must be adequate to penetrate vehicle components to be detected by the receiver. Generally, no hard wiring from the vicinity of the wheels to the receiver is required when utilizing such an RF communications link. When relying on robust RF coupling between the individual transmitters (or transponders) and a central receiver (or interrogator), techniques should be provided to prevent xe2x80x9cfalse alarmsxe2x80x9d, such as a low tire pressure signal emitted by a transmitter of another vehicle in close proximity to the vehicle in question. Additionally, it is sometimes desirable to be able to ascertain which of the several (e.g., four) tires on a given vehicle has a sensed low pressure condition.
U.S. Pat. No. 3,533,060 (Garcia; 1970), incorporated in its entirety by reference herein, describes a pressure-responsive radio transmitter (13) disposed on each valve stem (21) of each tire (12) of a vehicle (11).
xe2x80x9cReceiving antennas 16 are mounted in each of the wheel wells and connected by appropriate leads to a receiver set 17 mounted on or attached to the dashboard of the vehicle 11 . . . the receiver set can be of standard construction and include amplifying means to amplify the signals picked up by the antennas 16 and means for indicating the occurrence of such transmission, in the form of a buzzer, a bell, a light, or the like.xe2x80x9d (column 2, lines 30-38)
U.S. Pat. No. 4,220,907 (Pappas, et al.; 1980), incorporated in its entirety by reference herein, discloses a low tire pressure alarm system for vehicles such as trucks and cars. Each wheel is provided with a transmitter (200). A common receiver (300) has either a single receiving antenna, or multiple antennas, with each wheel having a separate antenna (302a . . . 302d) associated therewith. As disclosed therein at (column 14, line 66 through column 15, line 3):
xe2x80x9cIf multiple antennas are provided, they would be optimally loops of fairly large size, located near each wheel . . . however . . . a ferrite loopstick will do, and that smaller dimension of this arrangement makes for a more convenient mounting packagexe2x80x9d
The possibility of two antennas at each wheel location is also discussed in this patent (column 15, lines 11-15). As shown in FIG. 15, four antennas 302a . . . 302d may be selected, one at a time, by an analog switch (304).
U.S. Pat. No. 5,541,574 (Lowe, et al., 1996), incorporated in its entirety by reference herein, discloses (at FIG. 11 thereof):
xe2x80x9cthe electrical circuitry for a single exciter/reader [interrogator] 92 is provided at a suitable location within the vehicle, and used to communicate with transponders (not shown) on each of the vehicle""s wheel assemblies 2a-2d. The output of the exciter/reader 92 is time shared between corresponding antenna coils 48a-48d adjacent each of the wheel sites. Only the antenna coils 48a-48d, and no electronics, are required at the localized wheel sites. This is facilitated by the extreme simplicity of the required signal protocol, and the large magnitude of the return signals. The exciter/reader 92 communicates with one tire transponder at a time, deactivating a given transponder before moving on to the next. xe2x80x9d (column 7, lines 51-64)
U.S. Pat. No. 5,731,754 (Lee Jr., et al.; 1998), incorporated in its entirety by reference herein, discloses an apparatus 10, comprising a transponder 18 and sensors, suitable for mounting within or on a vehicle tire and which operates to sense and transmit various tire condition parameters to a remote interrogation unit 80. As disclosed therein:
xe2x80x9cA transponder and sensor apparatus with on-board power supply is mounted in or on a vehicle tire. A pressure sensor, a temperature sensor and a tire rotation sensor are mounted in a housing along with the transponder, the power supply and an antenna. Upon receiving an interrogation signal from a remote interrogator, the transponder activates the sensors to sense tire pressure and temperature and then backscatter-modulates the radio frequency signal from the interrogator with the tire condition parameter data from the sensors to return the backscatter modulated signal to the interrogator.xe2x80x9d(Abstract)
The interrogator 80, as shown in FIG. 9 of U.S. Pat. No. 5,731,754, generates an interrogation signal which is transmitted by transmitter 84 over an antenna 85. The interrogation signal is received by the remotely located transponders 18, which respond using a backscatter modulation technique. The backscatter-modulated signal from the transponder 18 is passed by the antenna 85 to an input of a receiver 86, for decoding. In this manner,
xe2x80x9cthe tire condition parameter data from one or more apparatus 10 may then be output from the interrogator 80 to an external host computer 90 by suitable communication circuits including parallel, RS-232, RS-485 and ETHERNET communication circuits.xe2x80x9d (column 7, lines 55-59).
U.S. Pat. No. 5,790,016 (Konchin, et al.; 1998), incorporated in its entirety by reference herein, discloses a tire pressure sensing system. A sensor-transducer (14) is mounted within each tire, and is essentially a passive LC circuit with a pressure-sensitive switching element. A receiver (20) is mounted in proximity to each tire, and comprises inductors and an amplifier which together form an oscillator. The system continuously monitors air pressure within each of the tires during motion of the motor vehicle though generation of an electromagnetic coupling between corresponding pairs of sensor-transducers and receivers during an alignment that occurs between the transducers and couplers during each rotation of the tire. An indicator interface (80) is located within the passenger compartment of the motor vehicle, such as on the dashboard, and displays the current status of each of the vehicle tires, such as with LEDs, to the motor vehicle operator. Each receiver is connected to the indicator interface through wiring, or, alternatively, through a wireless communication link.
It is an aspect of the present invention to provide method and apparatus for monitoring an operating characteristic of a pneumatic tire, as defined in one or more of the appended claims and, as such, having the capability of being implemented in a manner to accomplish one or more of the subsidiary objects.
According to the invention, a Low Pressure Warning System (LPWS) comprises a xe2x80x9ctagxe2x80x9d associated with, and preferably disposed within, each tire of a vehicle. At least one sensor is associated with each tag, such as a pressure sensor. The tag is capable, in the least, of transmitting an RF signal modulated with information regarding measured air pressure within the tire, and may also include temperature data (in which case, a temperature sensor would also be associated with each tag). The RF signals from the tire tags are low-power, short range signals and, for each tag, are received by an associated monitor located in close proximity to the respective tire tag, such as within the respective wheel well of the vehicle. The monitor receives and demodulates the RF signal from the associated tire tag, and impresses a data signal indicative of tire temperature (and, optionally, pressure) on a data bus within the vehicle. An on-board vehicle computer is also connected to the data bus, to receive and interpret the data. A display is also connected to the data bus, to display the interpreted data, under direction of the computer. Optionally, the tag is also capable of receiving information on an RF signal transmitted by the associated monitor. Such a signal is generated by the monitor in response to a data signal impressed on the data bus by the computer. There is thus provided a method for measuring and monitoring tire pressure, and providing this information to a driver of the vehicle, including warning the driver when a low tire pressure condition occurs.
An advantage of the LPWS of the present invention is that the same design can be used in all types of vehicles from passenger cars to heavy duty vehicles, including trailers. The LPWS can be offered as an option by the vehicle manufacturer since it connects easily to (two wire plug-in connection, or 4 wires. Include power connections) and multiplexes its data to existing RS-485 (or the like) vehicle data buses.
Another advantage of the LPWS of the present invention is that all tire pressure (and temperature) data can be displayed on the common vehicle display, thereby eliminating a requirement for a dedicated tire parameter display.
Another advantage of the LPWS of the present invention is that it features a xe2x80x9cshort haulxe2x80x9d (close proximity) RF link (between the tire tag and the antenna of the associated LPWS monitor) rather than a xe2x80x9clong haulxe2x80x9d RF link. An advantage of xe2x80x9cshort haulxe2x80x9d is a short unobstructed signal path with resulting low power requirements and higher reliability, as well as other benefits of near field transmission.
Another advantage of the LPWS of the present invention is that, when receiving data the LPWS monitor removes the data from the RF signal and impresses the data directly onto the data bus, thereby eliminating any need for RF energy to be routed over the vehicle wiring. Conversely, when transmitting, the LPWS monitor generates its own RF, again obviating any need for RF energy to be routed over the vehicle wiring.
Other objects, features and advantages of the invention will become apparent from the description that follows.